The present invention relates to a method and a device for implementing the method of measuring the oil consumption of internal combustion engines in which the oil is radioactively labeled with tritium or other tracers and the exhaust gas is examined for the contents of such tracers.
Methods of measurement are known for assessments of the oil consumption (MTZ 32 (1971) 3, pages 84 to 90) which make use of the measurement of the oil volume or the oil weight for this purpose. Moreover, the determination of the oil consumption by means of labeling with .sup.3 H as a tracer and measurement of the .sup.3 H-consumption in the gas phase is known (Automobiltechnische Zeitschrift 73, No. 3. March 1971, pages 75 - 79). Since the former method of measurement is inaccurate and the results are falsified because of fuel dilution and oil foaming, and since the influence of volatility upon the oil consumption cannot be properly assessed when labeling the oil with Zn and Na tracers, the latter method of measurement must presently be regarded as the most favorable one for measuring oil consumption.
It uses labeling by tritium of the oil and measurement in the gas phase in a proportional counter, where a branch stream is continuously diverted from the exhaust gas of the engine and fed to the proportional counter together with a methane stream. The sump of the engine contains tritiated motor oil. Together with the oil consumption stream the activity stream reaches the exhaust gas and is carried along with it. An activity concentration will build up in the exhaust gas which can be measured in the detector.
However, in order to be able to measure the oil consumption one must determine the detector response probability, the specific activity of the oil to be measured and the volume flow of the exhaust gas; in addition, the following readings must be taken to determine the volume flow of the exhaust gas: volume flow of the intake air, intake pressure, air temperature, fuel density, fuel consumption stream, fuel temperature, exhaust gas temperature and exhaust gas density. Moreover, the detector response probability is not constant for all modes of operation of the engine. It varies on the order of more than 100 %. This is due, among other factors, to the different ionization capabilities caused by the composition of the exhaust gas, etc. Hence, for one engine run the response probability must be determined for all operating points of interest with a nontritiated motor oil and a defined addition of .sup.3 H. Afterwards, the same program must be run again with tritiated oil to measure the oil consumption.
The finite volume of the feed lines to the detector gives rise to a dead time of aproximately two minutes. As a result of the delay in mixing of the gases in the detector, the steady state value, which corresponds to the changed operating point, will appear only some 10 - 12 minutes after a change. Over this period of time the environment will necessarily be contaminated with tritium, which also applies to the measuring period proper, because for the time of the measurement the engine must be running and only a very small branch stream can be used for measurement. Also the trial run of the engine (capital investment and operating cost) is prolonged. High voltage fluctuations in the detector give rise to errors in measurement.